Sow fresh seed (germination is very poor from the previous year's seed) in a deeply-dug bed in 1-2cm deep drills. Choose a still day as seed are very light. Either sow thinly along the drill then thin to 15cm or sow three or four seeds every 15cm and thin to the strongest. Germination can be very slow - 2-4 weeks. Weed by hand or hoe very carefully to avoid damage which can cause canker. Water only lightly and then only in long dry spells to avoid the soil drying out - sudden heavy watering after a dry spell can cause splitting.
Lift as required with a fork, beginning when the leaves begin to die back. Frost will sweeten the roots but frozen ground will also make it difficult to dig them out, so lift and store a few in November to see you through the cold months. Lift any remaining roots by the end of March.